A quantum effect known as entanglement may be part of the compass that birds use to sense Earth’s magnetic field, researchers report in an upcoming Physical Review Letters.

Critters from bacteria to mole rats use tiny variations in the Earth’s magnetic field to navigate, but exactly how they sense the magnetism is a mystery. One idea is that magnetic fields disrupt pairs of entangled electrons in a light-sensitive protein in the retina. In quantum entanglement, particles are linked to each ...